U.S. President Barack Obama on Monday ruled out a shift in strategy in the fight against the Islamic State despite the deadly attacks in Paris last week, saying putting U.S. troops on the ground to combat the group "would be a mistake."

Obama, speaking at a news conference following a G20 leaders' summit in Turkey, said the U.S.-led coalition fighting Islamic State in Iraq and Syria would redouble efforts to implement its current strategy rather than moving in a new direction.

"There will be an intensification of the strategy that we put forward but the strategy that we put forward is the strategy that ultimately is going to work," Obama told reporters. "But ... it is going to take time."

"It is not just my view, but the view of my closest military and civilian advisers, that (boots on the ground) would be a mistake," the U.S. president added.

Obama said the coordinated attacks that killed 129 people in Paris on Friday were a setback in the fight against Islamic State, but he insisted the U.S.-led coalition was making progress in bringing down the militant group, which overran parts of Syria and Iraq last year.

He said U.S. intelligence agencies have been concerned about a potential attack on the West by Islamic State militants for over a year but they did not pick up specific threats about an attack on Paris that would have enabled officials there to respond effectively to deter the assault.

"There were no specific mentions of this particular attack that would give us a sense of something that we could provide French authorities, for example, or act on ourselves," he said.